1. Field of the invention
The present invention relates to a USB control device and its operation method, and more particularly to a USB control device and its operation method with a two-way connectivity embedded into a computer system.
2. Description of Related Art
Since the USB specification has the advantages of a plug-and-play function for connecting up to 127 USB devices, supplying a power of 5V, and occupying only one IRQ, the USB are used extensively by users. In existing computer systems, at least one USB port is provided for connecting external devices, and thus manufacturers adopts the concept of transmitting data between computers via a USB interface.
Since the USB interface is of master/client architecture, a data transmission between a computer and a peripheral is performed by a master function provided by the computer and a device function provided by the peripheral.
Therefore, some manufacturers integrate a bridge chip and a USB connecting line to form a USB connecting line with a bridge function, but such arrangement requires a bridge chip and thus incurs a higher cost, and the connecting line with the bridge function is only for a connection between computers. If it is necessary to connect a general USB device, a general USB connecting line is required, and thus the application is very inconvenient.
To solve the foregoing problem, related patents including R.O.C. Pat. No. M276282 entitled “Switching USB access device” are disclosed, and the USB access device 1 of such patent as shown in FIG. 1 comprises a USB interface unit 10, a USB controller 12, a function module 14 and a manual switch 16.
The function module 14 can be a memory for storing an active mode driver 140 and a passive mode driver 142, and the manual switch 16 is used for setting up the USB controller 12 to execute the active mode driver or the passive mode driver, and the USB controller 12 is switched to an active mode or a passive mode.
Further, R.O.C. Pat. No. 591509 entitled “USB control circuit applicable for computer transmissions and operation method thereof” is disclosed, and the USB control circuit of this patent comprises a server controller with a USB interface, a device function circuit and a path switching device, provided for users to specify or automatically detect a data transmission between computers. Users specify a connecting path of the path switching device according to the user's desired connecting peripheral device or according to a computer that would automatically decide on a connecting path, and the automatic decision preset a USB control circuit to be the default active mode, then according to the preset time interval used for setting up a USB control circuit the prior art automatically decide to operate by the active mode or by the device function mode.
When the aforementioned R.O.C. Pat. No. M276282 is practiced, it is necessary to add the manufacturing cost for installing a manual switch on the USB access device, and a user must manually switch to the desired operation mode when a switch is required. Thus, the application is very inconvenient and inefficient to users. The following shortcomings are found in the practice of the R.O.C. Pat. No. 591509. Firstly, the user specified way incurs a higher manufacturing cost for adding a switch. Secondly, an active mode is used for the initial state of the USB control circuit, and a predetermined time interval is used for switching a mode, and thus the setting of timing in the software must be very accurate. If the response time of a connected device exceeds the predetermined time interval, an uncertain status will occur.